Steel products and method for producing same



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Patented E ton, Zill, 153631 3,009,843 STEEL PRODUCTS AND METHOD FUR PRODUCKNG SAME Elliot S. Nachtinan, Park Forest, 111., and John E. ODon neil, Highland, lnd., assignors to LaSalle Steel Company, Hammond, lnd., a corporation of Delaware No Drawing. Filed Oct. 22, 1956, Ser. No. 617,267 13 Claims. (Cl. 148-12.1)

This invention relates to the improvement of mechan- ,provide a method applicable to the metallurgical processing of a hot-rolled steel, such as a steel of the type which strain-hardens and hardens by some mode of precipita- ,tion when worked at elevated temperatures to improve the physical and mechanical properties of the steel.

This application is an improvement over the copending applications Serial Nos. 518,411, 518,412, now Patent Nos. 2,767,837 and 2,767,835, respectively, both granted October 23, 1956. 518,413, and 518,414, now Patent Nos. 2.767.836 and 2,767,838. respectively, both granted October 23, 1956, filed by Nachtman and Moore on June 27, 1955.

In the aforementioned copending applications, the teaching is made of the new and improved concept for enhancing the physical and mechanical properties of steel by the combination of steps which includes the step of advancing the steel through a die to effect reduction in crosssectional area while the steel is at a temperature within the range of 200 F. to the lower critical temperature for the steel composition. This step is referred to hereinafter as the elevated-temperaure-reduction step, which is effected by working the steel to effect reduction in cross section while the steel is at a temperaure within the range of 200 F. to 1l00-l200 F. In accordance with the teaching of the aforementioned copending applications, the temperature employed in the elevated-temperature-reduction step influences the trend of improvements secured in physical and mechanical properties of the steel. By controlling temperature, chemistry, and the amount of reduction, it becomes possible selectively to vary physical and mechanical properties developed in the steel. The properties can be varied over a fairly' wide range while enhancing and improving the uniformity of physical and mechanical characteristics developed in steels of the same chemistry from heat to heat, as distinguished from the wide variation which normally exist in hot-rolled steels.

It has now been found that the high-strength levels secured by elevated-temperature reduction of steels, as defined in the aforementioned copending applications, can be maintained along with many of the other improvements made available in the steels by the elevated-tem peraturereduction step, and that still further improvements can be secured in the physical and mechanical properties of the steel to produce new and improved steel products when use is made of a combination of steps which includes heat-treating the steel after the elevated-temperature-reduction step.

As used herein, the term heat treatment after elevatedtemperature reduction is meant to include:

(1) Annealing the steel after the elevated-temperaturereduction step by heating the steel to annealing temperature or to a temperature in the range of 1400-1500 F.

followed by slow cooling, as by means of air, to room temperature similarly to the annealing step employed i1 advance of elevated-temperature reduction.

(2) Normalizing the steel after the elevated-tempera ture-reduction step by heating the steel to normalizin temperature or to a temperature (above the upper crit ical temperature of the steel) between 1300 and 1500 F. followed by rapidly cooling the steel to room tempera ture.

(3) Producing a phase change in the steel after th elevated-temperature-reduction step by' heating the stee to a temperature above the transformation range-tha is, to a temperature in the order of 1500-l600 P. am then quenching the steel .to room temperature to produc a phase change to martensite.

(4) Producing a phase change in the steel after takin the elevated-temperature-reduction step, as by heating th steel to a temperature above the transformation rang such as to a temperature withinthe range of 1500" ti 1600 F., quenching the austenitized steel and then tem pering the quenched steel by re-heating the steel to form tempered martensite.

(5) Processing the steel after the elevated-temperature reduction step by heating the steel to a temperature abov the transformation range, such as to a temperature with in the range of l500-l600 F., followed by a partie quench to a temperature within the range of 200 F. t the lower critical temperature for the steel compositior (6) Mar tempering the steel after taking the elevatet temperature reduction. as by heating the steel to a ten perature above the transformation range, that is, to temperature above 1500 F. and then quenching the stet in a bath maintained at a temperature in the upper poi tion of the temperature range for martensite formatio (M until the metal has reached that temperature an then the steel is allowed to cool through the range fc martensite formation to ambient temperature.

(7) Anstempering the steel after taking the elevatet temperature-reduction step by heating the steel to a ten perature above the transformation range, such as to temperature within the range of l5001600 F. fo lowed by quenching the steel in a bath maintained at temperature slightly above the M range and of a cha' acter which causes the extraction of heat from the stei at a rate which prevents passage of the steel throug the austenitic range or prevent high temperature tran: formation products. and maintaining the steel at a ten perature below that of pearlite formation but above th: of martensite formation. such, for example, as when ti steel is quenched in a salt bath maintained at a temper: ture of 640 F. followed by quenching to room temper; ture after the temperature of the steel has become un form at the temperature of the quench.

(8) Treating the steel by diffusion transfer, as, ft example, in the processes of carburizing, nitriding, cyz niding, chromizing, and carbonitriding the steel after tt steel has been processed to the elevated-tempcrature-n duction step. As used herein, the terms diffusion an carburizing are intended to have their normal meat ing in the steel trade. Diffusion can be defined brieli as involving the movement of atoms within a solutioi The net movement is usually in the direction from regior of high concentration towards regions of lower concei tration in the attempt to achieve homogeneity of tl system, which may be in a liquid or gas or, as in ft present instance, a solid metal. Carburizing is a ditli sion transfer process wherein carbon is introduced int the steel by bringing the steel into intimate contactlr relation with a carbonaceous material, in the form of solid, liquid or gas, and heating to a temperature aboi the transformation range for the steel and holding 1 The steel, at the desired elevated temperature, was then lubricated with a conventional drawing compound and advanced through the draw die to take a representative reduction in cross-sectional area. The 1144 steel, originally of 7%." round, was given a 21.6% reduction, while the 4140 steel, of round, was given a 19.9% reduction.

After the elevated-temperalure-reduction step, the steels were heated to austenitizing temperature for one hour. The temperature employed was 1500 F., and then the austenitized steels were quenched in oil to room temperature.

Table I Drawn to take a 21.0% reduction Austenitized at 1.500 F. for one hour Quenched to room temperature Ansten- Tensile Izod Hardness Temp. of draw, itizing strength, impact Warp- F. temp., psi. 70 F. age

F. ft.lbs. S MR 0 Table II Drawn to take a 19.9% reduction Austenitized at 1,500 F. for one hour Quenched to room temperature Austen- Tensile Izod Hardness Temp. of draw, itizing strength, impact Warp- F. temp, psi. 70 F. age

F. tt.-lbs. S MR 0 Hot roll 1, 500 205.000 23.7 680 429 438 203 Cold drawn 1, 500 250, 500 25. 3 636 502 470 211 640 1, 500 210, 000 32. 3 020 429 402 298 1,000 1, 500 204, 000 29. 7 619 429 386 256 Also included among the processes of heat treating after elevated temperature drawing is the process of stress relieving after elevated temperature drawing. This cycle representative of the teachings of this invention will be illustrated using Cll44 steel as before.

The steel after pickling and liming is drawn at elevated temperatures, allowed to cool to room temperature and subsequently reheated to the stress relieving temperature. Tables III and IV will illustrate results obtained using such a cycle with two different percent reductions in area.

Table III [C-114-t steel drawn to take a 20.3 percent reduction] It is to be understood that other temperatures than those illustrated in Tables Ill and 1V may be used in the teachings of this invention and although not the same, rolling of the steel may be carried out at the elevated temperature to produce similar results.

It will be apparent from the foregoing examples that steels having new and different properties are secured by the processing of the steels to take an elevated temper: ture reduction step followed by heat treating, as by auster itizing and quenching, stress relieving, etc. Steels havin reduced stress relationships and improved impact strengt't are secured while maintaining the strength levels of tli steel at a high level.

It will be understood that changes may be made in th details with respect to the methods of heating and coo ing the steel, or in the techniques of processing the stee through the various steps embodying the practice of th invention without departing from the spirit of this invet tion, especially as defined in the following claims.

I claim:

1. The metallurgical process for treating a hot rolle steel which strain hardens and hardens by some mode precipitation when worked at a temperature between 200 F. and the lower critical temperature for the hot rolle steel composition, consisting of the following combin: tion of steps in the order specified of advancing the stet through a die to effect reduction in cross-sectional are while the steel is at a temperature within the range 450 F. to the lower critical temperature for the stet composition, subjecting the steel to diffusion transfer sul sequent to the elevated temperature reduction step fo lowed by cooling to room temperature.

2. A steel product having new and improved physio and mechanical properties produced by the method claim 1.

3. The metallurgical process for treating a hot rolle steel which strain hardens and hardens by some mode 1 precipitation when worked at a temperature between 20( F. and the lower critical temperature for the hot rolle steel composition, consisting of the following combin tion of steps in the order specified of advancing the ste through a die to effect reduction in cross-sectional an while the steel is at a temperature within the range of 45( F. to the lower critical temperature for the steel comp sition, carburizing the steel and then cooling the ste to room temperature.

4. The metallurgical process for treating a hot TOllt steel which strain hardens and hardens by some mode I precipitation when worked at a temperature blWCt 200 F. and the lower critical temperature for the h rolled steel composition, consisting of the following cor bination of steps in the order specified of advancing ti steel through a die to effect reduction in cross-section area while the steel is at a temperature within the ran; of 450 F. to the lower critical temperature for the ste composition, nitriding the steel and then cooling the ste to room temperature.

5. The metallurgical process for treating a hot roll: steel which strain hardens and hardens by some mode 1 precipitation when worked at a temperature between 201 F. and the lower critical temperature for the hot roll: steel composition, consisting of the following combinatir of steps in the order specified of advancing the ste through a die to effect reduction in cross-sectional art while the steel is at a temperature within the range of 451 F. to the lower critical temperature of the steel compo: tion, cyaniding the steel and then cooling the steel to roo temperature.

6. The metallurgical process for treating a hot T0111 steel which strain hardens and hardens by some mode precipitation when worked at a temperature between 204 F. and the lower critical temperature for the hot roll steel composition, consisting of the following combinatit of steps in the order specified of advancing the ste through a die to effect reduction in-cross-sectional ar while the steel is at a temperature within the range 450 F. to the lower critical temperature for the ste composition, chromizing the steel and then cooling t steel to room temperature.

7. The metallurgical process for treating a hot roll steel which strain hardens and hardens by some mode precipitation when worked at a temperature between 20 F. and the lower critical temperature for the hot rolled steel composition, consisting of the following combination of steps in order specified of advancing the steel through a die to effect reduction in cross-sectional area while the steel is at a temperature within the range of 450 F. to the lower critical temperature for the steel composition, carbonitriding the steel and then cooling the steel to room temperature.

8. The metallurgical process for treating a steel which strain hardens and hardens by some mode of prccicitation when worked at a temperature between 200 F. and the lower critical temperature for the steel composition consisting of the following combination of steps in the order specified of advancing the steel through a draw die to effect a reduction in crosssectional area while the steel is at a temperature within the range of 450 F. to the lower critical temperature for the steel composition, subjecting the steel to diffusion transfer subsequent to the elevated temperature reduction step, followed by cooling to room temperature.

9. The metallurgical process for treating a steel which strain hardens and hardens by some mode of precipitation when worked at a temperature between 200 F. and the lower critical temperature for the steel composition consisting of the following combination of steps in the order specified of advancing the steel through a draw die to effect reduction in cross-sectional area while the steel is at a temperature within the range of 450 F. to the lower critical temperature for the steel composition, carburizing the steel, and then cooling the steel to room temperature.

10. The metallurgical process for treating a steel which strain hardens and hardens by some mode of precipitation when worked at a temperature between 200 F. and the lower critical temperature for the steel composition consisting of the following combination of steps in the order specified of advancing the steel through a draw die to effect reduction in cross-sectional area while the steel is at a temperature within the range of 450 F. to the lower critical temperature for the steel composition, nitriding the steel, and then cooling the steel to room temperature.

11. The meallurgical process for treating a steel which strain hardens and hardens by some mode of precipitation when worked at a temperature between 200 F. and the lower critical temperature for the steel composition consisting of the following combination of steps in the order specified of advancing the steel through a draw die to effect reduction in cross-sectional area while the steel is at a temperature within the range of 450 F. to the lower critical temperature for the steel composition, cyaniding the steel, and then cooling the steel to room temperature.

12. The metallurgical process for treating a steel which strain hardens and hardens by some mode of precipitation when worked at a temperature between 200 F. and the lower critical temperature for the steel composition con sisting of the following combination of steps in the order specified of advancing the steel through a draw die to effect reduction in cross-sectional area while the steel is at a temperature within the range of 450 F. to the lower critical temperature for the steel composition, chromizing the steel, and then cooling the steel to room temperature.

13. The metallurgical process for treating a steel which strain hardens and hardens by some mode of precipitation when worked at a temperature between 200 F. and the lower critical temperature for the steel composition consisting of the following combination of steps in the order specified of advancing the steel through a draw die to effect reduction in cross-sectional area while the steel is at a temperature within the range of 450 F. to the lower critical temperature of the steel composition, carbonitriding the steel, and then cooling the steel to room temperature.

References Cited in the file of this patent UNITED STATES PATENTS 2,183,358 Six Dec. 12, 1939 2,462,851 Fawcett et al. Mar. 1, 1949 2,531,731 Hibbert Nov. 28, 1950 2,717,846 Harvey Sept. 13, 1955 2,767,837 Nachtman Oct. 23, 1956 OTHER REFERENCES Dunn: Iron & Steel Eng, pages 51-57 and 77, July 1946.

Pomp: The Manufacture and Properties of Steel Wire, 1941, English ed., 1954, pages 92-93.

Metals Handbook, pp. 684-685, 1948 edition.

The Manufacture and Properties of Steel Wire, pp. 58 and 252-256, Pomp, 1954.

The Manufacture and Properties of Steel Wire, Pomp, page 93, 1954. 

1. THE METALLURGICAL PROCESS FOR RTREATING A HOT ROLLED STEEL WHICH STRAIN HARDNESS AND HARDENS BY SOME MODE OF PRECIPITATION WHEN WORKED AT A TEMPERATURE BETWEEN 200* F. AND THE LOWER CRITICAL TEMPERATURE FOR THE HOT ROLLED STEEL COMPOSITION, CONSISTING OF THE FOLLOWING COMBINATION OF STEPS IN THE ORDER SPECIFIED OF ADVANCING THE STEEL THROUGH A DIE TO EFFECT REDUCTION IN CROSS-SECTIONAL AREA WHILE THE STEEL IS AT A TEMPERATURE WITHIN THE RANGE OF 450* F. TO THE LOWER CRITICAL TEMPERATURE FOR THE STEEL COMPOSITION, SUBJECTING THE STEEL TO DIFFUSION TRANSFER SUBSEQUENT TO THE ELEVATED TEMPERATURE REDUCTION STEP FOLLOWED BY COOLING TO ROOM TEMPERATURE. 